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• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C227/00—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton
  • C07C227/26—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton from compounds containing carboxyl groups by reaction with HCN, or a salt thereof, and amines, or from aminonitriles
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C255/00—Carboxylic acid nitriles
  • C07C255/01—Carboxylic acid nitriles having cyano groups bound to acyclic carbon atoms
  • C07C255/24—Carboxylic acid nitriles having cyano groups bound to acyclic carbon atoms containing cyano groups and singly-bound nitrogen atoms, not being further bound to other hetero atoms, bound to the same saturated acyclic carbon skeleton
  • C07C255/29—Carboxylic acid nitriles having cyano groups bound to acyclic carbon atoms containing cyano groups and singly-bound nitrogen atoms, not being further bound to other hetero atoms, bound to the same saturated acyclic carbon skeleton containing cyano groups and acylated amino groups bound to the carbon skeleton
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C227/00—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton
  • C07C227/04—Formation of amino groups in compounds containing carboxyl groups
  • C07C227/10—Formation of amino groups in compounds containing carboxyl groups with simultaneously increasing the number of carbon atoms in the carbon skeleton
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C227/00—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton
  • C07C227/14—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton from compounds containing already amino and carboxyl groups or derivatives thereof
  • C07C227/16—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton from compounds containing already amino and carboxyl groups or derivatives thereof by reactions not involving the amino or carboxyl groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C227/00—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton
  • C07C227/14—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton from compounds containing already amino and carboxyl groups or derivatives thereof
  • C07C227/18—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton from compounds containing already amino and carboxyl groups or derivatives thereof by reactions involving amino or carboxyl groups, e.g. hydrolysis of esters or amides, by formation of halides, salts or esters
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C227/00—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton
  • C07C227/22—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton from lactams, cyclic ketones or cyclic oximes, e.g. by reactions involving Beckmann rearrangement
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C227/00—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton
  • C07C227/38—Separation; Purification; Stabilisation; Use of additives
  • C07C227/40—Separation; Purification
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C227/00—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton
  • C07C227/38—Separation; Purification; Stabilisation; Use of additives
  • C07C227/40—Separation; Purification
  • C07C227/42—Crystallisation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C253/00—Preparation of carboxylic acid nitriles
  • C07C253/30—Preparation of carboxylic acid nitriles by reactions not involving the formation of cyano groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C255/00—Carboxylic acid nitriles
  • C07C255/01—Carboxylic acid nitriles having cyano groups bound to acyclic carbon atoms
  • C07C255/24—Carboxylic acid nitriles having cyano groups bound to acyclic carbon atoms containing cyano groups and singly-bound nitrogen atoms, not being further bound to other hetero atoms, bound to the same saturated acyclic carbon skeleton
  • C07C255/28—Carboxylic acid nitriles having cyano groups bound to acyclic carbon atoms containing cyano groups and singly-bound nitrogen atoms, not being further bound to other hetero atoms, bound to the same saturated acyclic carbon skeleton containing cyano groups, amino groups and carboxyl groups, other than cyano groups, bound to the carbon skeleton

Definitions

• the present invention relates to novel processes and synthetic intermediates for the preparation of ⁇ -difluoromethyl ornithine.
• Eflornithine or ⁇ -difluoromethylornithine has recently been approved in the United States in a topical cream for removing unwanted facial hair. Efficient, scaleable syntheses of DFMO are therefor useful to provide manufacturing
• the invention relates to processes for the preparation of DFMO, having the formula
• the processes include the step of selectively reducing a nitrile moiety of a compound of the formula
• R 1 is linear or branched C 1 to C 4 alkyl and Z is (i) —NH 2 or (ii) a protected amino moiety selected from the group consisting of
• R 2 is hydrogen, linear or branched C 1 to C 4 alkyl or aryl
• R 4 is linear or branched C 1 to C 4 alkyl, alkoxy or aryl.
• ester and amide (including the lactam) moieties of formulas 7, 9, or 10 are hydrolyzed to give the compound of formula 1.
• the invention relates to intermediates useful in the preparation of DFMO.
• the intermediates include compounds of the formula
• R 5 is:
• R 2 is hydrogen, linear or branched C 1 to C 4 alkyl or aryl
• R 4 is linear or branched C 1 to C 4 alkyl, alkoxy or aryl.
• Preferred intermediates include: ethyl 2-benzylideneamino-2-difluoromethyl-4-cyanobutanoate, ethyl 2-(diphenylmethylene)amino-2-difluoromethyl-4-cyanobutanoate, ethyl 2-amino-2-difluoromethyl-4-cyanobutanoate, or ethyl 2-acetylamino-2-difluoromethyl-4-cyanobutanoate, or salts thereof.
• DFMO difluoromethyl ornithine
• the processes of the invention have been developed from readily available and inexpensive starting materials. Furthermore, the processes provide high yields of DFMO, simplify isolation and purification steps, and minimize the use of halogenated solvents.
• an alkyl glycine ester of the formula 2 serves as a convenient starting material for a short synthesis of an alkyl 2-difluoromethyl-4-cyanobutanoate intermediate (compound of the formula 5) wherein R 1 is C 1 to C 4 linear or branched alkyl and R 2 is hydrogen, C 1 to C 4 linear or branched alkyl, or aryl.
• Compound of the formula 5 can then be converted by a number of processes to DFMO.
• the compound of formula 3 can be obtained from the glycine ester of the formula H 2 NCH 2 CO 2 R 1 , (formula 2) wherein R 1 is C 1 to C 4 alkyl.
• R 1 is C 1 to C 4 alkyl.
• the alkyl group is methyl, ethyl, or t-butyl.
• Glycine ethyl ester for example, is readily available from a number of commercial vendors as its hydrochloride salt.
• the compound of the formula 3 can be formed by treatment of the glycine ester of the formula 1 with an aryl aldehyde or ketone of the formula PhC(O)R 2 , wherein R 2 is hydrogen, C 1 to C 4 alkyl or aryl (Scheme 1).
• a dehydrating agent such as magnesium sulfate or sodium sulfate can optionally be used to remove the water generated in the reaction.
• a tertiary amine base e.g., triethylamine (TEA), tributylamine (TBA) or N,N-diisopropylethylamine, can be included in the reaction mixture to generate the neutral form of the ester.
• reaction conditions can provide high yields and conversions, preferably >98% for both yield and conversion, of compound of the formula 3.
• the condensation reaction can also be accomplished using an aprotic solvent, e.g., xylene or toluene (preferably toluene), and catalytic amount of a Lewis acid, e.g., boron trifluoride etherate, triphenyl boron, zinc chloride, aluminum chloride, and the like.
• aprotic solvent e.g., xylene or toluene (preferably toluene)
• a Lewis acid e.g., boron trifluoride etherate, triphenyl boron, zinc chloride, aluminum chloride, and the like.
• the condensation reaction can include the use of a Dean Stark trap and/or the use of other such dehydrating techniques known to those of ordinary skill to hasten the reaction rate by removing the formed water effectively.
• the alkyl 4-cyanobutanoate of the formula 4 is, in one embodiment, obtained from the compound of the formula 3 by a Michael reaction.
• compound of the formula 3 is treated with acrylonitrile, a base such as potassium carbonate and a phase transfer catalyst (PTC), such as triethylbenzylammonium chloride, tetrabutylammonium chloride, tetraethylammonium chloride, or trimethylbenzylammonium chloride at temperatures of from about 10 to about 45° C., preferably from about 20 to 35° C.
• PTC phase transfer catalyst
• the compound of formula 4 is then alkylated using a strong base and a halodifluoromethane alkylating reagent to form the compound of formula 5.
• Suitable strong bases include those that are effective in deprotonating the compound of formula 4 at the position ⁇ to the carboxylate.
• Examples of strong bases include alkali metal alkoxides of the formula MOR 3 wherein M is Na, Li or K and R 3 is C 1 to C 4 linear or branched alkyl; alkali metal hydrides, or alkali metal amide (e.g., sodium amide, sodium bistrimethylsilylamides).
• the alkoxide base is either a sodium or potassium alkoxide, more preferably a sodium alkoxide, such as sodium ethoxide or sodium t-butoxide.
• a slight molar excess of base is used in the reaction such as from about 1.6 to 2.0 equivalents.
• the alkylation reaction is carried out, for example, by deprotonation at a temperature of from about ⁇ 35 to about 25° C.
• Useful halodifluoromethane alkylating reagents include difluoroiodomethane, chlorodifluoromethane, or bromodifluoromethane.
• the halodifluoromethyl alkylating reagent is chlorodifluoromethane.
• halodifluoromethyl alkylating reagent typically an excess of the halodifluoromethyl alkylating reagent is used in the reaction such as from about 1.05 to about 2.0 molar equivalents. In instances where the alkylation reaction is run in a pressure vessel, smaller amounts of the halodifluoromethyl alkylating agent are used.
• the alkylation reaction is carried out in suitable aprotic solvents such as dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethylsulfoxide, or an ether such as tetrahydrofuran, 2-methyltetrahydrofuran, methyl t-butyl ether, diethyl ether, dioxane, or mixtures thereof.
• suitable aprotic solvents such as dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethylsulfoxide, or an ether such as tetrahydrofuran, 2-methyltetrahydrofuran, methyl t-butyl ether, diethyl ether, dioxane, or mixtures thereof.
• the solvent used in this alkylation reaction is an ether, preferably tetrahydrofuran or tetrahydrofuran/acetonitrile.
• the synthetic steps include: hydrolysis of the Schiff's base protecting group, reduction of the nitrile moiety and hydrolysis of the alkyl ester moiety.
• the Schiff's base protecting group of the compound of the formula 5 is hydrolyzed by treatment with an aqueous acid using conditions well known in the art, to provide the compound of formula 6.
• Suitable acids include mineral acids, toluenesulfonic acid, methanesulfonic acid, trifluoroacetic acid, and the like.
• the reaction is conveniently carried out in a mixture of the aqueous acid and an organic solvent.
• the compound of the formula 6 is then converted to the diamino compound of formula 7 by reduction of the nitrile moiety.
• Any reduction procedure effective to selectively reduce the nitrile moiety to the amine with minimal competing ester reduction can be used.
• heterogeneous transition metal catalysts are effective catalysts for the hydrogenation of the nitrile moiety.
• an acid such as hydrochloric acid is added to the reaction mixture.
• the transition metal catalysts include, for example, palladium on carbon, platinum on carbon, and platinum oxide.
• the catalyst used in the reduction is 5-10% platinum on carbon.
• the amount of hydrochloric acid typically used in the reaction is 1 to 5 equivalents, more preferably 3 to 4 equivalents.
• the reaction solvent for the hydrogenation can be an alcohol, preferably ethanol or an ether, preferably t-butyl methyl ether.
• the reaction is carried out in a suitable corrosive resistant reaction vessel such as a Hastelloy bomb vessel with hydrogen at a pressure of, for example, from about 80 to about 120 psi.
• the hydrogenation is typically run at temperatures from about 25 to about 40° C., preferably about 25 to 30° C.
• DFMO can be obtained by hydrolysis of the alkyl ester moiety of the diamino compound of the formula 7.
• the alkyl ester moiety can be hydrolyzed using aqueous basic conditions well known to those of ordinary skill in the art.
• the alkyl ester moiety can be hydrolyzed using acidic conditions.
• Suitable acids for the hydrolysis reaction include mineral acids or toluene sulfonic acid.
• the hydrolysis is effected using an excess of mineral acid, for example 12 N HCl at reflux.
• the t-butyl ester can also be hydrolyzed by milder acidic hydrolysis methods well known in the art, such as treatment with formic acid or trifluoroacetic acid.
• DFMO can be conveniently isolated as its monohydrochloride monohydrate salt.
• a solution of from about 9 to about 13% by weight DFMO in about a 1 to 3-3.5 mixture of aqueous hydrochloric acid 12 N and alcohol, preferably ethanol, is provided with a pH of less than 0.5.
• the resulting solution can be treated with sufficient triethylamine to effect a pH of about 4 to form a slurry containing precipitated DFMO dihydrochloride.
• the precipitated DFMO hydrochloride monohydrate is recovered by methods well known to those of ordinary skill in the art including filtration and centrifugation.
• the crude DFMO recovered can be further purified by recrystallization from suitable recrystallizing solvents such as ethanol/water.
• the purity of the DFMO is at least 98%, more preferably at least 99% pure.
• metal hydride reagents can be used to effect the selective reduction of the nitrile moiety.
• hydride reagents include NaBH 3 (O 2 CCF 3 ) and other such modified borohydride and aluminum hydride reagents that selectively reduce the nitrile moiety in the presence of a carboxylic ester moiety.
• the ester moiety of the amino compound of formula 6 is hydrolyzed before reducing the nitrile group with a metal hydride.
• a metal hydride For example the alkyl ester of the amino compound of formula 6 is saponified to give a carboxylate salt.
• the nitrile is then selectively reduced to the amine by treatment with hydride reagents such as NaBH 3 (O 2 CCF 3 ), and other such modified borohydride and aluminum hydride reagents that selectively reduce the nitrile moiety in the presence of a carboxylic acid or acid salt.
• the compound of formula 5 is directly hydrogenated to form the diamino compound of formula 7 using a heterogeneous transition metal catalyst, e.g., platinum on carbon, using hydrochloric acid and a solvent such as ethanol.
• a heterogeneous transition metal catalyst e.g., platinum on carbon
• the compound of the formula 6 is converted to the compound of formula 1 via the lactam compound of the formula 10 (Scheme 3).
• Base metal catalysts effective for the nitrile reduction include nickel-, cobalt-, or copper-aluminum alloy catalysts.
• a preferred catalyst is a cobalt-aluminum alloy catalyst such as that sold as Raney cobalt catalyst by Engelhard Corporation.
• Suitable solvents for the reduction include ethanol, methyl t-butyl ether, tetrahydrofuran, isopropanol, and the like.
• the lactam is hydrolyzed under basic conditions such as 10 N hydroxide solution or under acidic conditions using a suitably strong acid such as 12 N HCl.
• a suitably strong acid such as 12 N HCl.
• the lactam is hydrolyzed under acidic conditions using a mineral acid.
• DFMO is conveniently isolated as its monohydrochloride monohydrate salt as described above.
• the nitrile moiety of the compound of the formula 5 (preferably wherein R 2 is aryl) is reduced to an amine before the 2-amino protecting group is removed (Scheme 4).
• Compound of the formula 5 is treated with a base metal catalyst to reduce the nitrile moiety and provide the compound of the formula 11.
• Base metal catalysts that can be used for this reduction reaction include nickel-, cobalt-, or copper-aluminum alloy catalysts.
• the catalyst is a cobalt-aluminum alloy catalyst.
• Solvents useful in the reduction reaction include alcohols, e.g., ethanol and ethers, e.g., methyl t-butyl ether.
• the Schiff's base can be removed by acid hydrolysis, as described above for Process A, and the ester group is further removed to complete the preparation of DFMO.
• the amino protecting group in the compound of formula 5 is switched from a Schiff's base protecting group to an amide (or carbamate) protecting group (Scheme 5).
• the compound of the formula 8, wherein R 4 is linear or branched C 1 to C 4 alkyl, alkoxy or aryl, is obtained by treating the compound of formula 5 with suitable acylating reagents.
• the acylating agents include anhydrides, acid chlorides, chloroformates, activated esters, e.g. N-hydroxysuccinimide esters, or other acylating agents well known to those of ordinary skill in the art.
• the acylating reagent is acetic anhydride so that R 4 is methyl in the compound of formula 8.
• the acylation reaction can be performed in ethers, dimethylformamide, dimethylacetamide, esters (e.g., ethyl acetate) as well as other solvents, in the presence of an organic base such as triethylamine or pyridine.
• the nitrile group of the compound of formula 8 is then reduced using procedures analogous to those described above for Process A to provide the compound of formula 9.
• the compound of formula 9 can be isolated and further purified, it can be conveniently used in the next step without further purification.
• the ester and amide moieties of the compound of formula 9 are hydrolyzed to provide DFMO.
• the hydrolysis can be accomplished by first hydrolyzing the carboxylic acid ester moiety with aqueous base followed by acid hydrolysis of the amide moiety with, for example, mineral acids.
• both the ester and amide moieties are hydrolyzed simultaneously using acidic conditions, e.g., 12 N HCl.
• DFMO can be isolated and further purified as its monohydrochloride monohydrate salt as described above.
• the compound of formula 1 or its synthetic precursors can be resolved into its individual isomers by resolution techniques well-known to those of ordinary skill in the art.
• the lactam of the compound of formula can be formed, i.e., the compound of formula 10, and then the acid addition salt of the lactam can be prepared with a homochiral acid such as (+) or ( ⁇ ) binaphthylphosphoric acid as described in U.S. Pat. No. 4,309,442.
• Other resolving agents i.e., homochiral acids, well-known in the art could also be employed.
• chiral reversed phase chromatography techniques can be used to resolve the product if desired.
• DFMO is typically produced by the process of the invention as a salt.
• the salt can be exchanged by a pharmaceutically acceptable salt as needed to provide the desired formulation.
• the vessel was then de-pressurized and its contents filtered through diatomaceous earth (Celite®).
• the diatomaceous earth was washed with MTBE and methanol, and the filtrate was concentrated under vacuum to yield 5.53 g of crude product (103.4% weight yield, estimated ⁇ 75% pure by 1 H NMR).
• the reaction was cooled to ambient temperature, and the slurry was filtered and washed with 200 mL acetonitrile.
• the filtrate was transferred to a 2 L reactor equipped with a thermocouple and mechanical agitation.
• the filtrate was concentrated to a volume of ca. 300 mL.
• the reactor was charged with THF (400 mL), purged with N 2 , and cooled to ⁇ 20° C.
• NaOtBu (53.9 g, 561.1 mmol, 1.5 eq) was dissolved in THF (560 mL) and the mixture was cooled to ⁇ 25° C.
• the cold NaOtBu solution was charged to the reactor over 3-4 min
• the reaction was agitated for a total of 7-10 min then chlorodifluoromethane (Freon-22®) was charged via a sparge tube at such a rate as to maintain the reaction temperature ⁇ 10° C.
• the reaction was judged complete with the end of the exotherm and the simultaneous change in color from dark red-black to light brown.
• the reaction mixture was allowed to warm to 20-25° C. then concentrated to a volume of ca. 500 mL.
• the reaction mixture was charged with EtOAc (600 mL) and H 2 O (600 mL). The resulting mixture was agitated, and the phases were separated.
• the rich EtOAc solution was concentrated to a volume of ca. 300 mL.
• EtOH 400 mL was charged and the mixture was concentrated again to a volume of ca. 300 mL.
• the solvent swap was repeated with an EtOH charge (400 mL), and the solution was concentrated to a final volume of ca. 500 mL.
• the rich EtOH solution was cooled to 0-5° C. After a slurry started to form, the solution was agitated for 15 min.
• H 2 O 156 mL was charged at such a rate as to maintain the slurry temperature ⁇ 5° C. After complete addition of H 2 O, the slurry was agitated for 5-10 mins. The cold slurry was filtered and the cake was washed with ⁇ 10° C. EtOH/H 2 O (200 mL, 50:50).
• aryl shall mean a phenyl or substituted phenyl.
• Preferred phenyl substituents include C 1 to C 6 alkyl, C 1 to C 6 alkoxy and halogen.

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